Age-related macular degeneration, a common cause of blindness, has been linked to an increased risk of heart attack and stroke.

Researchers found the risk of dying from the cardiovascular conditions was at least doubled in people with AMD.

The study raises the possibility - disputed by UK experts - that drugs for the condition may be to blame.

The University of Sydney research appears in the British Journal of Ophthalmology.

AGE-RELATED MACULAR DEGENERATION

There are two forms - wet and dry - with the dry form being far more common

The wet type is the most aggressive and accounts for around 90% of blindness caused by the condition

More than 20,000 people in the UK are newly-diagnosed with wet AMD each year

AMD affects the centre of the retina (macula) at the back of the eye, which is used for fine central vision tasks, such as reading and driving.

It is most common in the elderly, among whom it is a major cause of untreatable blindness in developed countries. It is estimated to affect 500,000 people in the UK alone.

The Sydney team assessed the general and eye health of over 3,600 people, all aged at least 49 years at the start of the study.

Of these 2,335 people were re-examined five years later, and 1,952 were examined again 10 years later.

Among people under the age of 75 at the start of the study, early AMD was associated with a doubling in the risks of dying from a heart attack or stroke within the next decade.

Those with late stage disease at the start of the study had five times the risk of dying from a heart attack, and 10 times the risk of dying from a stroke.

Possible reasons

The researchers admitted that more work was needed to confirm their work, as the numbers in their study were relatively small.

They said the reason for a link between AMD and cardiovascular disease was unclear.

The likely reason for the link is vascular degeneration

Mr Winfried AmoakuRoyal College of Ophthalmologists

It could simply be that AMD is a sign that the body is ageing, and vulnerable to all sorts of disease.

Alternatively, it may be that AMD and cardiovascular disease are caused by the same problems, such as inflammation, thickening of the arteries or general tissue damage caused by unstable particles called free radicals.

Another possibility is that anti-VEGF drug treatments for AMD may raise the risk of heart attack and stroke.

Anti-VEGF drugs work by inhibiting the growth of new blood vessels.

This is an effective strategy for AMD because the condition is caused by unstable new blood vessels in the eye, which leak fluid and blood under the retina and cause scarring, which in turn leads to irreversible sight loss.

However, there is concern that inhibiting blood vessel growth may have a wider impact on the cardiovascular system.

Monitoring

The researchers said: "Our results suggest that individuals with a high cardiovascular risk profile may potentially need to be monitored closely if receiving anti-VEGF therapy."

The National Institute for Health and Clinical Excellence (NICE) eased restrictions on NHS use of one of the anti-VEGF drugs, Lucentis last year, following a campaign to make it more widely available to AMD patients.

Mr Winfried Amoaku, of the Royal College of Ophthalmologists, said other research had also suggested a link between AMD and cardiovascular disease.

But he said anti-VEGF drugs approved for UK use had been shown to be safe.

He said: "The likely reason for the link is vascular degeneration. This is a systemic failure that can affect several parts of the body in relatively quick succession."

The RNIB said the study had not established that the drugs raised the risk of cardiovascular disease, and urged patients not to be put off seeking treatment.

Novartis, the makers of Lucentis, said the drug was very effective, and had proved safe in major clinical trials.

Inflammation genes

A second study in the same journal highlights variations in genes that control the production of chemicals involved in inflammation as a possible key to AMD.

A team from the University of Southampton examined variations in genes controlling production and suppression of cytokines - powerful chemicals involved in inflammatory processes in the body.

They compared DNA samples from people with AMD to those who showed no signs of the disease.

One particular gene variant was significantly more common in the people with AMD.